For clarity, and to make merging easier.

The code to manage the hash table of "pending resync EOFs" for append-only
tables is moved to smgr_ao.c. One notable change here is that the
pendingDeletesPerformed flag is removed. It was used to track whether there
are any pending deletes, or any pending AO table resyncs, but we might as
well check the pending delete list and the pending syncs hash table
directly, it's hardly any slower than checking a separate boolean.

There are still plenty of GPDB changes in smgr.c, but this is a good step
forward.

This bumps the copyright years to the appropriate years after not
having been updated for some time.  Also reformats existing code
headers to match the upstream style to ensure consistency.

Also update all uses of the name in the code as well as pgindent
file.

This is addressing the GPDB_83_MERGE_FIXME comment in xact.c:1081.

GPDB doesn't need `haveNonTemp` check, since GPDB doesn't allow data loss.

GPDB doesn't support the asynchronous commits from upstream because this might
cause data inconsistency across segments in a cluster.

We disable the support of async commit using macro IMPLEMENT_ASYNC_COMMIT.
And make the user GUC `synchronous_commit` as DEFUNCT_OPTIONS, so that its
setting will be ignored, and a WARNING is generated.

The original check for temp table in smgrGetPendingFileSysWork() is not valid
in GPDB, since GPDB temp table use shared buffers to support access across slices.

Once GPDB decide to support async commit, this macro can be removed.
Signed-off-by: NXin Zhang <xzhang@pivotal.io>

It's very error prone to externally maintain variable to track
maxTID for a table, need to worry about lot of cases like vacuum and all.
Persistent tables historically used this mechanism to perform certain
checks, which seem irrelevant now that we are freeing tuples in
regular heap way for persistent tables as well.

I found these with "callcatcher", written by Caolán McNamara. Many thanks
for the tool! See https://www.skynet.ie/~caolan/Packages/callcatcher.html